1. Field of the Invention
The present invention relates to a vehicle positioning method and its system, especially to a vehicle positioning method and its system being used under the environment without Global Positioning System (hereinafter GPS) signals or with weak GPS signals.
2. Description of Related Art
In general, a conventional vehicle positioning system is a GPS navigation system 50. With reference to FIG. 7, the GPS navigation system 50 has a GPS module 52 and an IMU (Inertial Measurement Unit) module (not numbered). The GPS Module 52 receives positioning information from multiple satellites, and the positioning information comprises driving data including at least longitude, latitude, direction, and speed of the vehicle on which the GPS module 52 is mounted. The IMU module has a gyroscope 51, an accelerometer 53, an Euler angle estimator 54, a navigation acceleration unit 55, and a navigation speed-calculation unit 56, so the IMU module outputs current vehicle inertial data including driving direction, speed and so on. The final GPS coordinates of the vehicle are decided by the GPS navigation system 50 according to the positioning information of the GPS module 52 and the vehicle inertial data from the IMU module. For example, the GPS navigation system 50 uses the driving direction and speed from the IMU module and corrects the direction and speed from the GPS module 52.
The GPS module 52 cannot provide the available driving data when the vehicle is located at the environment without GPS signals or with weak GPS signals, such as a location under a bridge or in the building. Although the GPS navigation system 50 may obtain a last available driving data before the vehicle is driving into the building and cooperates with the vehicle inertial data from the IMU module to generate the GPS coordinates, inaccurate GPS coordinates may be calculated since the sensing errors of the IMU module are accumulated.
US patent publication No. 20110121068, which is incorporated as referenced herein, discloses a method and apparatus for determining position and rotational orientation of an object. With reference to FIG. 8, the apparatus has multiple barcode marks 61, multiple reference position patterns 60 and multiple cameras 62. Each barcode mark 61 has a unique ID. Each camera 62 is mounted on a corresponding moveable object. The reference position patterns 60 are mounted on a ceiling of an indoor space in which the moveable objects are moving. The reference position patterns 60 are arranged in multiple crossed lines. The barcode marks 61 are mounted on the reference position patterns 60 and are arranged in a matrix. When one moveable object is moving into the indoor space, the camera 62 of the moveable object captures the reference position patterns 60 and at least one of the barcode marks 61 thereon. Then, the 2D axes and the ID of the captured barcode mark 61 are obtained. The current position of the moveable object is determined according to the 2D axes and the ID of the captured barcode mark 61, so that the moveable object can be controlled to move along a preset path inside the indoor space.
The above-mentioned conventional apparatus can determine a current position of the moveable object in the indoor space, but the conventional apparatus is only applied for the object moving along a preset path indoors. Therefore, the reference patterns 60 and the barcode marks 61 have to be fixed on the ceiling. The coordinates of the object are calculated by a relationship of the reference patterns 60 and the barcode marks 61 to further position the object. However, the coordinates system is only applied to a specific area. Again, the conventional apparatus can provide the movable position information, but the movable position information cannot be used as the position information of the GPS navigation system or a cruise control system. Therefore, the positioning accuracy of the GPS navigation system or the cruise control system used in the environment without GPS signals or having weak GPS signals has to be improved.